The use of a turbocharger or twin turbochargers has become more prevalent as manufacturers seek to improve the output performance of various internal combustion engine configurations. The turbocharger is frequently given preference in the exhaust aftertreatment system over various exhaust aftertreatment devices. By preference, it is meant that the turbocharger is located upstream of the various exhaust aftertreatment devices, such as the oxidation catalyst, in order to maximize the energy input to, and output available from, the turbocharger. In this arrangement, catalyst light-off is delayed by the thermal load associated with the turbocharger and by locating the exhaust aftertreatment devices, particularly the oxidation catalyst, farther from the exhaust ports. Thus, on engine start-up, it takes longer for the exhaust aftertreatment devices to reach their operating temperatures and perform their emission treatment functions. This delay may be even further exacerbated in twin turbocharger configurations, particularly sequential twin turbocharger configurations where it is desirable to closely couple both turbochargers to maximize their energy output. Such configurations can require that the exhaust aftertreatment devices be placed even further downstream, which further delays catalyst light-off due to the increased distance of these devices from the exhaust ports. This characteristic of turbocharged internal combustion engines, particularly sequential twin turbocharger engine configurations, runs contrary to the general desire in current exhaust aftertreatment systems to light-off the catalyst as quickly as possible, or within a predetermined time period, in order to ensure compliance with tailpipe emissions requirements, particularly at engine start-up.
Accordingly, it is desirable to provide turbocharged internal combustion engine configurations that also provide exhaust aftertreatment systems that provide for rapid catalyst light-off.